Conventional image forming apparatuses include those in which a cleaning means is constantly cleaning the image carrier and those that do not have a cleaning means. In a conventional image forming apparatus in which a cleaning means is constantly cleaning the image carrier, a problem arises in that the image carrier and the cleaning means have short useful lives. In addition, in a conventional image forming apparatus that does not have a cleaning means, a problem occurs in that some matter may remain affixed to the image carrier, preventing a satisfactory image from being subsequently obtained.
One object of the present invention, therefore, is to provide an image forming apparatus in which a satisfactory image can be obtained and in which the image carrier and the cleaning means have long useful lives.
The foregoing problem is particularly noticeable in a tandem-type image forming apparatus, which forms a color image on a single sheet of paper by sequentially forming and combining color images of different colors by means of multiple image forming units. In addition to a color mode in which color images are formed, this type of image forming apparatus has an image creation condition in which only a portion of the image forming units are used, e.g., a monochrome mode in which images of a selected single color only are formed. The image forming units are naturally driven in unison during the color mode. They are also driven in unison during a monochrome mode in which some of the image forming units are not used, so that mutual synchronization is maintained.
When a conventional color image forming apparatus is not operating in the color mode, the cleaner blades of the image forming units that are not carrying out image creation sometimes become curled and cause damage to the photoreceptors. Problems resulting from this damage include the occurrence of image noise and excessive wear to the photoreceptive layers of the photoreceptors, resulting in a reduction in the useful lives of the photoreceptors. This is due to the fact that, during image creation in the monochrome mode, the cleaner blades continue to clean the image carriers of the image forming units that are not being used even when there is no remaining matter on them. While in principle it may be possible to move the cleaning blades out of contact with those image carriers whose image forming units are not being used, in practice this is not feasible since it causes a significant difference in the torques on the respective image carriers, which could result in a loss of synchronization between them and therefore poor image quality. Consequently, it is preferable to maintain the cleaning blades in constant contact with the image carriers. However, this constant contact results in scraping the surfaces of the photoreceptors and reducing their useful lives, as well as making the photoreceptor surfaces extremely smooth. This causes the photoreceptors to adhere to the cleaner blades, resulting in increased frictional resistance and curling of the cleaner blades. The problems of wear and damage to the image carriers, image noise and short useful lives remain even if cleaning rollers, cleaning brushes, magnetic brush rollers, etc. are used for the cleaning means instead of cleaner blades.
It is another object of the present invention, therefore, to provide a color image forming apparatus that minimizes the effects of wasteful cleaning, prevents the occurrence of image noise and prolongs the useful lives of the photoreceptors.